6-1 Chapter 6 - Datapath and Control

Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Principles of Computer ArchitectureMiles Murdocca and Vincent Heuring

Chapter 6: Datapath and Control

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Chapter Contents

6.1 Basics of the Microarchitecture

6.2 A Microarchitecture for the ARC

6.3 Hardwired Control

6.4 Case Study: The VHDL Hardware Description Language

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

The Fetch-Execute Cycle

• The steps that the control unit carries out in executing a program are:

(1) Fetch the next instruction to be executed from memory.

(2) Decode the opcode.

(3) Read operand(s) from main memory, if any.

(4) Execute the instruction and store results.

(5) Go to step 1.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

High Level View of Microarchitecture• The microarchitecture consists of the control unit and

the programmer-visible registers, functional units such as the ALU, and any additional registers that may be required by the control unit.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

ARC Instruction Subset

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

ARC Instruction Formats

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

ARC Datapath

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

ARC ALU Operations

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Block Diagram of ALU

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Gate-Level Layout of Barrel Shifter

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Truth Table for (Most of the) ALU LUTs

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Design of Register %r1

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Outputs to Control Unit fromRegister %ir

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Microarch-itecture of the ARC

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Microword Format

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Settings for the COND Field of the Microword

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

DECODE Format for Microinstruction Address

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Timing Relationships for the Registers

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Partial ARC

Micro-program

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Partial ARC Microprogram

(cont’)

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Branch Decoding• Decoding tree for

branch instructions shows corresponding microprogram lines:

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Assembled ARC

Microprogram

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Assembled ARC

Microprogram (cont’)

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Example: Add the subcc Instruction• Consider adding instruction subcc (subtract) to the ARC instruction

set. subcc uses the Arithmetic format and op3 = 001100.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Branch Table• A branch table for trap handlers and interrupt service routines:

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Microprogramming vs. Nanoprogramming

• (a) Micropro-gramming vs. (b) nano-programming.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Hardware Description Language

• HDL sequence for a resettable modulo 4 counter.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Circuit Derived from HDL

• Logic design for a modulo 4 counter described in HDL.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

HDL for ARC

• HDL description of the ARC control unit.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

HDL for ARC (cont’)

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

HDL ARC Circuit

• The hardwired control section of the ARC: generation of the control signals.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

HDL ARC Circuit (cont’)• Hardwired

control section of the ARC: signals from the data section of the control unit to the datapath.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

Case Study: The VHDL Hardware Description Language

• The majority function. a) truth table, b) AND-OR implementation, c) black box representation.

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

VHDL SpecificationInterface specification for the majority component

-- Interfaceentity MAJORITY is port

(A_IN, B_IN, C_IN: in BIT F_OUT: out BIT);

end MAJORITY;Behavioral model for the majority component -- Body

architecture LOGIC_SPEC of MAJORITY isbegin-- compute the output using a Boolean expressionF_OUT <= (not A_IN and B_IN and C_IN) or

(A_IN and not B_IN and C_IN) or(A_IN and B_IN and not C_IN) or(A_IN and B_IN and C_IN) after 4 ns;

end LOGIC_SPEC;

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

VHDL Specification (cont’)-- Package declaration, in library WORKpackage LOGIC_GATES iscomponent AND3 port (A, B, C : in BIT; X : out BIT);end component;component OR4 port (A, B, C, D : in BIT; X : out BIT);end component;component NOT1 port (A : in BIT; X : out BIT);end component;-- Interfaceentity MAJORITY is port

(A_IN, B_IN, C_IN: in BITF_OUT: out BIT);

end MAJORITY;

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Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring

VHDL Specification (cont’)-- Body-- Uses components declared in package LOGIC_GATES -- in the WORK library-- import all the components in WORK.LOGIC_GATESuse WORK.LOGIC_GATES.all architecture LOGIC_SPEC of MAJORITY is-- declare signals used internally in MAJORITYsignal A_BAR, B_BAR, C_BAR, I1, I2, I3, I4: BIT;begin-- connect the logic gatesNOT_1 : NOT1 port map (A_IN, A_BAR);NOT_2 : NOT1 port map (B_IN, B_BAR);NOT_3 : NOT1 port map (C_IN, C_BAR);AND_1 : AND3 port map (A_BAR, B_IN, C_IN, I1);AND_2 : AND3 port map (A_IN, B_BAR, C_IN, I2);AND_3 : AND3 port map (A_IN, B_IN, C_BAR, I3);AND_4 : AND3 port map (A_IN, B_IN, C_IN, I4);OR_1 : OR3 port map (I1, I2, I3, I4, F_OUT);end LOGIC_SPEC;